MadAss 125 - Help me with a noise

[carldjohnston]

Hi All,

New MadAss 125 owner here, recently picked up a 125 with a 140 upgrade; looks to have OORacing parts, new cylinder, head, carb, CDI etc. I've wanted one since they came out, and this popped up but needed some work.

Owner said there was a grinding noise when running, and we couldn't start it when I went to take a look. Had good compression and it turned over, but turned out the slide in the carb was stuck fully raised. Soon started after I fixed that.

So I heard the noise, and assumed it would be pretty obvious once stripped right down. Once apart I:
- Replaced the gearbox and selector forks, as there was a broken tooth on one gear, and the forks were worn - I assumed that this would be the cause of the noise.
- Noticed the piston had some small nicks consistent with dropping / ham fisting it, but cleaned them up; also shows slight wear marks down the sides
- Noticed the bore was slightly scored, and has some nicks that marry up with the nicks on the piston. It's overall very smooth though.
- The large driven gear (gearbox input) has nicks on the raised sections on the inside of the gear; looks to have touched the selector cam at some point
- Everything else seemed OK to me.

Problem is I have just started it up, and the noise is still there; so it wasn't the gearbox unfortunately..

Thinking that it could be the gearbox input driven gear, I removed the clutch and associated gears; but the noise persists, which rules out the gearbox.

I made a short video that shows the noise quite clearly: MadAss Motor Noise - YouTube

Could someone please point me in the right direction; I don't mind replacing the piston/bore, or the crankshaft, but would rather not continue to replace parts unnecessarily.

Thanks in advance!

Carl

 

[my67xr]

On the big driven gear, if you try turning it with the gearbox in first can you feel any movement there ?

the gear has some rubber bush's inside it, if they fail then it can cause it to be noisy.
You would also notice lots of black rubber bits in the oil filter strainer.

 

[carldjohnston]

There does seem to be some slack, but from the splines; the driven gear feels quite solid.

I have run the motor without the clutch, so this gear should be stationary, and the noise persists.

 

[my67xr]

ok, have you checked the flywheel nut is tight ? L/H side of the engine behind the cover
If the flywheel nut is tight, then i guess it's time to take the head off and check where there's movement, big end bearing or crank bearings maybe ?

Sort of sounds like valves hitting the piston too ?

 

[carldjohnston]

Thanks mate, I've only just put the motor back together after replacing the gearbox; the flywheel nut should be tight (went on with a rattle gun). The piston doesn't show any impact from valves, only slight scoring down the sides; the valves look to be good too.

Any tips on checking the bearings? What sort of play (if any) should be noticeable? Are the crankshaft bearings replaceable?

 

[my67xr]

Here is the Madass 125 service manual, it lists the crank clearances side to side and radial, and the limits of wear on page 74
http://www.cobrasales.com/docs/MadAss 125 Service Manual.pdf

found this too, similar noise maybe, they suggested clutch or crank bearings, but the guy didnt post up if he fixed it or not
I can see how it would put extra load on the crank bearings
The MadAss Army ? View topic - noisy engine with clutch disengaged

 

[carldjohnston]

Just put the bike back together, ended up getting some parts from OORacing as the local retailers wouldn't respond. Replaced the crankshaft as the con rod bearing was shot, and put a new oil pump in also. The con rod appeared to be contacting the crankshaft web, which I assume was the cause of the noise.

Thanks for your help, wish me luck with the RWC!